Web tension controlling rewind drive



April 14, 1970 H. E. FALLIS 3, 8

WEB TENSIONCONTROLLING REWIND DRIVE Eiled June 24. 1965 4 Sheets-Sheet 1 m2; wzjwmm noaol NOISNBJ.

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' A ril 14, 1910 Eff-E. F'Amsj I WEB TENSION CONTROLLING-'REWIND DRIVE 4 Sheets-Sheet 2 Filed June 24, 19 5 moE aw M W wt INVENTOR HAROLD E. FALLIS gmwd ATTORNEYS BY A A M, M w

April 14, 1970 .H. E. FALLls WEB TENSI ON CONTROLLING REWIND DRIVE Filed June 24. 1965 4 Sheets-Sheet 3 INVENTOR EDS-Z5 HAROLD. E. FALLIS gmm) ATTORNEYS United States Patent 3,506,863 WEB TENSION CONTROLLING REWIND DRIVE Harold E. Fallis, Mount Vernon, Ohio, assignor to Continental Can Company, Inc., New York, N.Y., a corporationof New York Filed June 24, 1965, Ser. No. 466,600 Int. Cl. H02k 49/08 US. Cl. 310-94 26 Claims ABSTRACT OF THE DISCLOSURE Web tension control provisions for use in reeling or unreeling a continuous web include a reel drive motor,.an electro-magnetic clutch coupling the motor with a reel, web tension sensing provision and a feed-back circuit for controlling the coupling of the electro-magnetic clutch in response to web tension variations indicated by the web tension sensing provision. The feed-back circuit may include a low-gain amplifier and provides less than full tension variation compensation to allow gradual changing in web tension during a winding or unwinding operation. Speed monitoring provisions detect the input and output speeds of the clutch, which speeds are compared and employed to control motor control provisions for maintaining a speed difierential between the input and the output of the clutch.

This invention relates to a tension control apparatus for winding or reeling material upon a rotary reel and more specifically to an apparatus and method for sensing the tension'of the material, such as a web, strip, wire, etc., being wound upon a reel and utilizing the signal so generated which is related to the material tension, to actuate a clutch which is in driving engagement with the reel. Although the embodiment shown and described has been directed to reeling or winding operations, it will be understood that the invention has equal applicability to unwinding and unreeling operations.

'In many winding and reeling operations, webs of great widths and lengths are advanced from an input reel, through a machine which may perform various functions and operations to the web, and finally to an output reel where the web is stored for removal to its final location. Such an operation just described may be one wherein thin films such as polyethylene, Saran, cellophane, etc. are printed in multicolors for ultimate use as flexible packages. If the operation is to be truly successful, then the unreeling, printing and reeling must be accomplished at a fast rate. However, it will be intuitively clear that the winding and reeling of thin films or sheets of material upon heavy reels, which may exceed 1000 pounds in weight, presents many problems.

It is desirable that the material be wound upon the reel in such a manner so as to present a neat and pleasant appearing reel, pleasing to ones esthetic sense, without ragged edges, fold over of the material, etc. If the reel is driven at a rate in excess at which the material is being delivered to the reel, then the material may be severed or parted so that the operation must be shut down in order to join the ends oft he parted material. If the reel is driven too slowly, then successive sections of the material about the circumference of the reel may cause inner sections of the material to be folded over, mutilated, or damaged.

In winding and reeling operations, it is known that if a reel is wound with the material being applied to the reel at a constant tension, then the material will tend to telescope, i.e., a condition wherein the material tends to elongate and be driven outwardly about the longitudinal axis of the reel due to the compressive forces of suc- 3,506,863 Patented Apr. 14, 1970 cessive outer bands of the material on the reel. In other words, the reel tends to assume the form of a telescope wherein the longitudinal center of the reel is displaced so that a cross section of the material would be in the form of a V.

On the other hand, if the reel is wound wherein a constant torque is applied to the reel, then the material upon the reel becomes too loose as the diameter of the reel increases. Under these conditions, outer bands of the material may cause damage to inner bands of material by causing the looseness to be taken up by fold-overs, stretching. etc.

Accordingly, since a reel wound with the material at a constant tension causes telescoping of the reel and a reel wound wherein a constant torque is applied to the reel produces looseness of the material upon the reel, it becomes desirable that a system be provided wherein the material is wound upon the reel under conditions somewhere between the constant tension system and a .constant torque system, i.e., wound with a decreasing tension, an increasing torque, or combinations of these parameters.

In most error detection and correction systems, an error is detected, whether it be an error of velocity, frequency, amplitude, tension, etc., and the correction system attempts to insert a correction factor wherein the original conditions will be maintained. Although many systems of this type possess high degrees of efliciency and stability, the correction system can usually never achieve correction due to such conditions as transients, losses, etc.; however, many systems do achieve a correction approaching 100%. In the present invention, we do not wish to employ a highly efiicient correction system in that a highly efficient correction system would provide a reel wherein the material is wound, (a) with a constant tension, which we wish to avoid or, (b) a reel wherein a constant torque is applied to the reel during the winding process, and, which, we also wish to avoid. Accordingly, it a control and correction system is employed which does not provide complete correction, then the desired characteristics of the material on the reel, according to the teaching of the present invention, will be achieved. It has been found that the desired characteristics are provided wherein an amplifier having low gain capabilities is employed in the correction portion of the winding and reeling system.

Accordingly, it is the principal object of the present invention to improve error detection and correction systems and methods.

'It is a further object of the present invention to provide error detection and correction apparatus and methods relating to the reeling and unreeling of a continuous length of material upon a reel.

It is a further object of the present invention to provide a winding and reeling apparatus and method which avoids the disadvantages of both'constant torque and constant tension systems.

It is a further object of the present invention to provide a winding and reeling system which employs an amplifier having low gain characteristics to achieve a winding and reeling operation wherein the material is wound upon the reel with decreasing tension, and increasing torque or combinations of changing tension and torque.

It is a further object of the present invention to provide a winding and reeling system wherein a signal is generated which is related to the material tension adjacent the reel, the signal being employed to control the actuation of a clutch for driving the reel.

It is a further object of the present invention to provide a winding and reeling system wherein a signal is generated which is related to the material tension adjacent the reel, the signal being applied to a low gain amplifier in circuit with an electric clutch for driving the reel.

It is a further object of the present invention to provide a winding and reeling system wherein a signal is generated which is related to the material tension adjacent the reel, the signal being applied to a low gain amplifier to control the output thereof and controlling, according to its output, the actuation of an electrically operated clutch for driving the reel.

It is a further object of the present invention to provide a winding and reeling system wherein a signal is generated which is related to the material tension adjacent the reel, the signal being applied to a transistor amplifier for controlling the amount of feedback applied thereto, which amplifiercontrols an electromagnetic clutch for driving a reel, the clutch being in the emitter-collector circuit of the amplifier.

It is a still further object of the present invention to provide a winding and reeling system wherein a signal is generated which is related to the material tension adjacent the reel, the signal being employed to control the actuation of an electromagnetic clutch for driving the reel, the output r.p.m. of the clutch being continuously monitored so that the input r.p.m. to the clutch is controlled in such a manner that it exceeds its output by a prescribed amount.

These and other objects of the present invention are provided by positioning a pair of web tension load sensors adjacent the reel as the web or other material is being wound (or unwound) upon the reel. The output from the web tension sensors is directed to a clutch control circuit which controls the current and its degree of coupling, through an electromagnetic clutch. The clutch may be of the magnetic fluid type, the eddy current slip clutch type, or dry powdered iron type. If the signal from the web tension sensors indicates that the tension at the particular moment is too great, then the clutch will supply less torque so as not to exceed he desired tension. On the other hand, if the web tension sensors indicate that the tension is not sufiicient, then the clutch control circuitry will provide a greater current to the clutch so as to increase the torque and thereby provide the desired tension of the material upon the reel being wound.

If the input shaft to the electromagnetic clutch far exceeds the revolutions per unit time than the output shaft of the clutch, then heating, Wasted energy, excessive wear and other problems may be encountered. This condition is alleviated by positioning a first tachometer to generate a signal related to the output r.p.m. of the clutch and a second tachometer to generate a signal indicating the input revolutions to the clutch. A circuit is provided to accept the two tachometer signals so as to control the motor supplying the rotary motion of the clutch with an r.p.m. only slightly in excess of the r.p.m. of the output of the clutch. In the preferred embodiment of the invention, it was found that an input r.p.m. of 110% of the output r.p.m. provided the necessary acceleration that may be needed without undue heating or other deleterious effects.

A salient feature of the invention is the employment of a low gain amplifier, such as a common-emitter transistor type, whose gain, or amount of feedback is manually adjusted and whose output is determined by the signals being generated by the web tension sensors. The clutch is included in the emitter-collector circuit of the amplifier and as such, provides a fast response to any undesired changes in tension of the web. As the tension of the web starts to change, the output of the transistor amplifier likewise changes so that the tension of the web is automatically adjusted and returned to the desired value. The circuitry does not provide a reel wherein the web of material is wound with a constant tension but one wherein only a partial correction is effected so that the tension decreases as the diameter of the reel increases which prevents the condition known as telescoping described earlier. Manual means are provided in the clutch control circuit for initially setting the gain of the amplifier, for providing a minimum tension to the web, for providing an initial tension to the web, and for providing the tension range.

In addition to the foregoing, a meter may be provided and calibrated for indicating the tension in pounds and a recorder for producing a permanent record of the tension.

The invention both as to its organization and method of operation together with further objects and advantages thereof will best be understood by reference to the following specification taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a graph of torque versus reeling time and of tension versus reeling time;

FIGURE 2 is a block diagram of the invention;

FIGURE 3 is an electrical schematic of the web tension sensors and control shown in block form in the FIG- URE 2;

FIGURE 4 is an electrical schematic of the clutch control circuit and the clutch shown in block diagram in the FIGURE 2; and

FIGURE 5 is an electrical schematic of the motor and clutch sensors shown in block form in the FIG- URE 2.

With reference tot he FIGURE 1, a graph is shown wherein reeling time is deployed ast he abscissa and the ordinate, is indicated as torque in the lower portion and tension in the upper portion. With initial reference to the torque versus reeling time of the graph, a constant torque line is shown which is substantially parallel to the abscissa. The constant torque line indicates that a reel is being wound wherein a constant and substantially unvarying torque is applied to the reel. Under these conditions, it has been found that the bands of the material or web being wound upon the reel becomes too loose as the diameter of the reel increases. This condition, of course, is undesirable in that inner bands of the material may be folded over or damaged by successive bands of the material as they are placed upon the reel.

In dotted outline of the torque versus reeling time graph of the FIGURE 1, is shown a curve with increasing torque along with increasing time. Although the increasing torque has been shown as a substantial straight line, it will be understood that a curve may be generated which departs substantially from the straight line but in general does indicate an increasing torque with increasing time. Under these conditions, the looseness of the web of material upon the reel would be reduced so that a snugly wound reel of material would be achieved.

In the tension versus reeling time portion of the graph of the FIGURE 1, a constant tension line is indicated which would be the proper showing of a reel wound wherein a constant tension is applied to the web as it is being wound. Previosuly, it was discussed that webs wound under these conditions produced unsatisfactory results in that the outer bands of material were wound much more tightly upon the reel as the diameter of the reel increased so that the reel tended to telescope. This, of course, is also undesirable and the same graph further depicts a dotted line indicating a decreasing tension with increasing reeling time so that the outer bands are not wound so tightly as to force the inner bands of material to be*displaced and thereby cause the condition of telescoping as previously set forth. Although the decreasing tension line is shown as a substantially straight line, it will be readily understood that the curve may depart substantially from the straight line but still generally indicate a decreasing tension with increasing time.

Since both the constant tension and constant torque devices produce unsatisfactory results, as set forth in the FIGURE 1, the system to be hereinafter set forth with reference to the following figures illustrates an apparatus and method for placing continuous bands of material about a reel with an increasing torque being applied to the reel in order to overcome the objection of the looseness of the outer bands of materal upon the reel, and a decreasing tension in order to overcome the objection of the tightness of the outer bands which cause the condition of telescoping.

As shown in the FIGURE 2 and in greater detail in the FIGURE 3, a web is advanced through a web tension sensors and control station 12. Although the web 10 is indicated as being a web, it will be readily understood that a wire, sheet, etc., could also be employed in the practice of the invention. The web tension sensors and control station 12 includes the electronic circuitry illustrtaed in the FIGURE 3 and in the FIGURE 2, a first roller 14, a second roller 16 which is positioned above and to the left of the roller 14, and a third roller 18 which is positioned substantially in line and to the left of the roller 14. It is about the rollers 14, 16 and 18 that the web 10 is advanced and when sensors are coupled to the shaft of one of the rollers, such as the roller 16, the tension of the web 10 may be measured.

The web 10 is then advanced from the roller 18 and wound about a reel 20 which is driven by an electromagnetic clutch 22, the electromagnetic clutch being discussed in greater detail with subsequent reference to the FIGURE 4.

With continued reference to the FIGURE 2, the tension of the web 10 is indicated on a pair of conductors 24 and 26 to a clutch control circuit 28, which clutch control circuit 28 is illustrated in greater detail in the FIGURE 4. Connected between the conductor 24 and the conductor 26 is resistor 30, a meter 32, and a parallel coupled resistor 34 and recorder 36. The clutch control circuit 28 controls the electromagnetic clutch 22 via a pair of conductors 38 and 40.

A motor 42 under control of a motor controller 44 provides rotational energy to the clutch 22 by a shaft 46. The clutch 22 is coupled to the reel 22 via a shaft 48. In order that a sufiicient p.r.m. be delivered by the clutch 22 upon the shaft 48, it is necessary that the motor 42 deliver upon its shaft 46, revolutions per unit time exceeding that delivered by the clutch 22. Accordingly, a reference tachometer 50 is positioned upon and adjacent the shaft 48 so as to indicate the revolutions per unit time of the shaft 48. The reference tachometer 50 includes a generating means 52, which may be a gear or sprocket having projecting teeth that affect a pickup head 54 positioned adjacent the generating means 52. Signals indicative of the revolutions per unit time of the shaft 48 are indicated on a pair of conductors 56 and 58 to a motor and clutch sensors circuit 60. In addition, a feedback tachometer 62, similar to the reference tachometer 50, is utilized to monitor the revolutions per unit time supplied by the motor 42 via the shaft 46 to the clutch 22. The feedback tachometer 62 includes a generating means 64, which also may be a gear or sprocket having projecting teeth which affect a pickup head 66. An output indicative of the revolutions per unit time delivered to the clutch 22 appears on a pair of conductors 68 and 70 to the motor and clutch sensors circuit 60. The motor controller 44 is under control of the motor and clutch sensors circuit 60 and communicates therewith by a pair of conductors 72 and 74. Electrical energy in the form of an alternating current or a direct current of sufficient magnitude is supplied to the motor controller circuit 44, as shown.

The function of the circuit illustrated in the FIGURE 3 is to supply a signal via the conductors 24 and 26 to the clutch control circuit 28 of the FIGURE 4 which is related to the tension being applied to the web 10 by the force utilized to rotate the reel 20. The tension being applied to the web 10 is measured by a load ring A and a load ring B which are positioned juxtaposed the shaft of the roller 16 and are responsive to any vertical movement of the shaft of the roller 16, the movement being caused by the tension applied to the web 10. Any movement of the load ring A is detected by the transformer comprised of the inductors 76, 78 and 80. The transformer primary winding 76 is connected to a conductor 82 at ground potential by a conductor 84 and to an oscillator output transformer 128 via a conductor 86. The secondary windings 78 and 80 of the load ring A are coupled in bucking arrangement and with the ring in the balanced or neutral position, the output is zero. The winding 80 is coupled to the conductor 82 at ground potential by a conductor 88 and also to one end of a resistor 90. Similarly, one end of the winding '78 is connected to a resistor 92 and to an operate switch 94 via a conductor 96. The opposite ends of the win-dings 78 and 80 are joined and coupled to the movable arm of a potentiometer 98, as shown. A grounded shield is provided about the conductors 88 and 96, as found necessary.

Force applied to the load ring A by the shaft of the roller 16 will shift the core or ring and cause an AC voltage to appear between the conductors 88 and 96. The resistors 90, 92 and 98 permit matching of the inductive and resistive components of the differential transformers which include the windings 76, 78 and 80 and its movable core identified as load ring A.

The load ring B of the FIGURE 3 is substantially identical to the load ring A and includes the inductors or windings 102, 104 and 106 which go to make up a differential transformer. Any movement of the load ring B by the opposite end of the shaft of the roller 16 will be detected by these windings. One end of the primary winding 102 is coupled to the conductor 82 at ground potential by a conductor 108 while the other end of the winding 102 is connected to the oscillator output transformer 128 via a conductor 110. The winding 104, a secondary winding, is connected to one end of the primary of a transformer 112 by a conductor 114 and also to a resistor 116. One end of the winding 106, the other secondary winding, is conected to the conductor 82 via a conductor 118 and also to a resistor 120. The opposite ends of the windings 104 and 106 are joined together to the movable arm of a potentiometer 122. A grounded shield 124 is provided about the conductors 114 and 118,

' as appropriate. In a manner similar to the circuitry about the load ring A, the secondary windings 104 and '106 are coupled in a bucking arrangement and the resistors 116, 118 and the potentiometer 122 permit matching the inductive and resistive components of the transformer. Force applied to the core or ring will shift the core and cause an AC voltage to appear across the conductors 114 and 118.

The secondary winding 127 of the transformer 128 is center-tapped and grounded and feeds the differential transformer primary windings 76 and 102, as shown. It will be noted that the other lead from the winding 102, namely, on the conductor 108, is at ground as is the conductor 84 from the primary winding 76. An input balance circuit is connected across the full secondary winding 127 of the transformer 128. The input balance circuit permits adding a bucking voltage in any quadrant so as to permit the adjustment of the meter to zero whenever the movable arms 144 and 148, to be hereinafter discussed, of the switch 140 is in the operate position, as shown. The conductors 86 and from the windings 76 and 102, respectively, are joined by a group of parallel components including the secondary winding 127 of the transformer 128, as previously indicated, and a pair of potentiometers 130 and 132. An oscillator 134 has its output coupled to the primary winding 129 of the transformer 128. Any convenient frequency of the oscillator 134 may be applied to the transformer 128; however, in an embodiment which was constructed and operated in accordance with the principles of the present invention, the frequency of the oscillator 134 was 5,000 cycles.

As shown in the FIGURE 3, the conductor 96 from the winding 78 is coupled to the operate switch 94 which is bridged by a resistor 136 Whose other end is coupled to the other end of the primary winding of the transformer 112 by a conductor 138. When the resistor 136 is in the circuit, it reduces the input to the amplifier so as to permit a zero adjustment of the meter 32. When the zero adjustment is almost complete, the switch 94 is closed and the final adjustment may be made without driving the meter 32 off scale.

During initial setting up operations, a switch is employed to provide a zero adjustment or input balance, which switch is indicated at 140 and has a first water 142 having a movable arm 144 and a second wafer 146 having a movable arm 148. The movable arms 144 and 148 are connected together so that they move to similar contacts on the wafers 142 and 146. Each of the wafers 142 and 146 have an off-contact, an A contact wherein the output from the load ring A is grounded out by its connection with the conductor 82 and the output from the load ring B is applied to the input transformer 112; a B contact wherein the output from the load ring B is grounded out by its conection with the conductor '82 and the output from the load ring A is applied to the input transformer 112; an A+B contact wherein the outputs from both the load rings A and B are applied to the input transformer 112; and, the operate contacts wherein the output from the input balance circuit is applied to the primary winding of the transformer 112 as well as the outputs from the load rings A and B. At specified times, the operate switch 94 is opened so as to insert a high value resistance 136 in the circuit and thereby prevent undue excursions of the meter 32. A conductor 150 extends from the operate contact of the wafer 146 and joins with the conductor 114 coupled to the lower side of the primary win-ding of the transformer 112. In addition, a conductor 152 extends from the operate contact of the wafer 142 and through a resistor 154 which is coupled to a movable arm 158 which is connected to a movable arm 1-60 of the potentiometer 132.

The meter amplification circuit of the FIGURE 3 includes the transistors T1, T2 and T3. A capacitor 162 bridges the secondary winding of the transformer 112 while one end of the secondary is coupled through a capacitor 164 to the base of the transistor T1. The other end of the secondary of the transformer 112 is connected to ground via the conductor 166. A bias voltage, for example, a voltage of 22 volts positive, is applied to the col lector of the transistor T1 through a resistor 168, to the collector of the transistor T2 by a resistor 170 and directly to the collector of the transistor T3.

The output across the resistor 168 is coupled from the collector of T1 to the base of T2 while the output developed across the resistor 170 is connected from the collector of T2 to the base T3. The base T1 is connected through a resistor 172 to the emitter of T2. The emitter of T2 is connected to ground by a resistor 174 which is by-passed by a capacitor 176. The emitter of T1 is connected to ground potential by the series resistors 178 and 180. The resistor 178 is by-passed by the by-pass capacitor 182 and the common point of the resistors 178 and 180 and one end of the capacitor 182 are connected to a calibrate adjust circuit which includes a series coupled potentiometer 184, a resistor 186, and a capacitor 188. An arm 190 of the potentiometer 184 is connected back to one end of the potentiometer 184. The other end of the capacitor 188 is connected to the base of the transistor T3, as shown. A parallel coupled resistor 192 and capacitor 194 are coupled to the primary of a transformer 196 while the opposite end of the transformer 196 is connected to ground, as shown.

The output from the secondary winding of the transformer 196 is rectified by the group of conventional diodes indicated at 198 with the rectified output being applied to the conductors 200 and 202. The conductor 202 is at ground potential to which is coupled an output terminal and conductor 26. A resistor 204 is in series with the conductor 200 and is directed to an output terminal and conductor 24. The conductors 24 and 26 are directed to the clutch control circuit of the FIGURE 4. A capacitor 206 is connected across the conductors 24 and 26 While a capacitor 208 is connected from the conductor 200 to ground. In addition, a series connected resistor 30, meter 32 and resistor 34 are coupled between the conductors 24 and 25 and 11 parallel with the capacitor 206. A recorder 36 is bridged across the resistor 34. The meter 32 may be calibrated so as to be supplied a voltage which is proportional to the pounds of tension on the web. This may be accomplished by any convenient means such as noting the position of the meter 32 for a particular tension and then measuring the tension with an instrument capable of directly denoting the pounds of tension at that particular meter setting. The recorder 36 will provide a permanent record, if desired, of the tension during the winding and reeling process.

As shown in the FIGURE 4, the output on the conductors 24 and 26 from the web tension sensors and control circuit 12 of the FIGURE 3 is applied to the low gain amplifier and its associated circuitry. The conductor 24 is coupled to the base of a transistor T4 by a resistor 210'. The conductor 26 is at ground, as shown. A potential, such as +40 volts is coupled through tension adjust potentiometer 212 and to ground. The arm of the tension adjust potentiometer 212 is connected through a resistor 214 to the base of the transistor T4. This is the reference voltage signal for the system.

The emitter of T4 is coupled to the base of a transistor T5 while the emitter of T5 is coupled to the base of a transistor T6. A negative voltage, such as a voltage of l5 volts, is connected to the emitter of T4 and the base of T5 via a resistor 216, directly to the collector of T5, and to the emitter of T6 by a resistor 218. A positive voltage, such as for example a voltage of 15 volts, is coupled directly to the collectors of T4 and T6 and to the emitter of T5 and base of T6 by a resistor 220. The output on the emitter of T6 is coupled to the base of a power transistor T7 via a resistor 222.

The transistors T4, T5 and T6 and their associated circuitry are coupled in emitter-follower configuration and are utilized as an impedance matching current amplifier. The reference signal voltage is derived from a high impedance potentiometer 212 and the foregoing circuitry exhibits an impedance match with the reference signal voltage source. The gain of the transistor T7 is manually controlled by a potentiometer 226 in the emitter circuit of T7, and will be discussed hereinafter. In other words, the amount of negative feedback is controlled by the potentiometer 226. The current through the circuitry is determinated by the potential at the base of the transistor stage T4 since the reference signal voltage from the potentiometer 212 and the input from the tension sensors at the terminal 24 are summed at the aforementioned base.

A salient feature of the invention is the utilization of a low gain amplifier such as that disclosed in the FIGURE 4 for controlling the current through the clutch 22 which drives the reel 20 through the shaft 48. The low gain characteristic of the amplifier is achieved by the relatively large emitter resistance (the potentiometer 226) of the transistor T7. It will be noted that the clutch 22 is included in the emitter-collector circuit of the transistor T7.

In the circuit of the FIGURE 4, the signal voltage applied to the base of the transistor T7=' causes a certain current to flow in the emitter-collector circuit. If resistance is inserted in the emitter circuit, then the emitter will end to follow the base and the smaller the resistance in the emitter circuit, the smaller the signal on the base that is required to produce relatively large changes in emitter current. A resistor 224 of low ohmic value is coupled to the emitter of T7 which is coupled to ground through a potentiometer 226 of low ohmic value. The

potentiometer 226 has its operating arm 228 connected to ground while its movable portion engages the resistance provided by the potentiometer 226. The potentiometer 226 serves as a taper adjustment or a manual gain control for the stage.

Also coupled to ground and through a conductor 38 is the clutch coil 22 which is in parallel with a series connected diode 230 and a resistor 232. The latter series elements serve to by-pass any large and perhaps harmful currents that are generated due to the large inductive effects to the clutch 22. The opposite end of the clutch winding 22 is coupled via a conductor 40 to a rectifier 234 via a conductor 236. The collector of T7 is connected to the other side of the rectifier 234 via a conductor 238 which includes the series inductance 240. A pair of capacitors 242 and 244 are coupled across the conductors 236 and 238, one on each side of the inductor 240. The components 240. 242 and 244 serve to smooth out and filter the rectified current from the rectifier 234 so as to provide stability and give a faster response to the amplifier.

In the FIGURE 4, a variable tap transformer is employed to supply different voltages to the rectifier 234 so that a different range of tension may be applied to the material by the clutch 22. Lighter webs of material will require lesser tensions than heavier webs of material. Accordingly, a transformer 246 having an input primary winding supplies a secondary winding having a plurality of taps such as the taps shown, which may be 20 volts, 40 volts, 60 volts and 80 volts. The secondary winding of the transformer 246 is coupled to the rectrifier 234 by the conductors 248 and 250. A movable contact 252 is connected to the conductor 250 and when in the position shown at the 80 volt tap, a higher range of tension will be provided than when the movable tap 252 is positioned at one of the lower voltage taps. A minimum range of tension would be applied when the movable tap 252 is moved to engage the 20 volt tap of the transformer 246.

In the FIGURE 4, a circuit is provided to supply a minimum voltage so as to rotate the reel 20 whenever no tension is being applied by the reel 20 and so indicated by the tension sensors. Whenever the voltage drop of the controlling circuit including the transistor T7 and its associated circuitry exceeds the drop of the minimum voltage circuit, to be hereinafter explained, the controlling circuit will take over. The minimum tension circuit includes a transformer 254 wherein a source of alternating current is supplied to its primary winding while its secondary winding is coupled via the conductor 256 and 258 to a rectifier 260. One output of the rectifier 260 is connected to ground 'by a conductor 262 while its other output is connected through a resistor 274, a potentiometer 266, a diode 268 and to the clutch winding 22 through the conductor 40. The diode 268 is poled, as shown, and a pair of capacitors 270 and 272 are connected on opposite ends of the resistor 274 and to ground at the conductor 262. A movable arm 264 has its fixed end connected to the cathode side of the diode 268 while its movable contact engages the impedance provided by the potentiometer 266. Adjustment of the movable arm 264 through experimentation, can be set to provide a minimum tension to be applied by the driving members coupled to the reel 20 to the web 10, best shown in the FIGURE 2.

The transistor T7 is coupled in a common emitter amplifier configuration and the emitter-base circuit is from the resistor 222, through the emitter of T7, the resistor 224 and the potentiometer 228 and then to ground. The voltage applied to the resistor 222 at the base of T7 may be either positive or negative depending upon whether the reference signal voltage or the signal voltage from the tension sensor is the larger. The collectoremitter circuit starts at ground and goes through the conductor 38, through the clutch coil 22 and power supply 10 260, the conductor 236, the full-wave rectifier 234, through the inductor 240 and via the conductor 238 is returned to the collector. The current flow through the aforementioned circuit is controlled by the signal at the base of T7 while the gain of T7 is manually controlled by adjusting the taper adjustment potentiometer 228.

The circuit of the FIGURE 5 is employed to control the input shhaft to the electromagnetic clutch 22 through the motor controller 44 and the motor 42 in accordance with the output shaft of the clutch 22. In other words, revolutions per unit time must be applied to the input shaft of the clutch 22 slightly in excess of the revolutions per unit time of the output shaft of the clutch. This, of course, is necessary in order that suflicient torque be available at all times in the event that the clutch control circuit 28 of the FIGURE 2 indicates that the revolutions per unit time applied to the reel 20 by the shaft 48 be increased. However, if the input revolutions are far in excess of the output revolutions, then deleterious effects are produced within the clutch 22 such as heating, excessive wear, etc. Therefore, the function of the FIG- URE 5 is to monitor the revolutions per unit time of the shaft 48 and the revolutions per unit time of the shaft 46 so as to maintain a substantially predetermined ratio between the revolutions of the two shafts. In the particular embodiment of the invention that was described and operated in accordance with the principles of the present invention, the revolutions per unit time of the input shaft 46 were approximately of the revolutions per unit time of the output shaft 48.

As shown in the FIGURE 5, the reference tachometer 50 supplies on the conductors 56 and 58 to a transformer 276, a series of signals related to the revolutions per unit of time of the shaft 48. Similarly, the feedback tachometer 62 supplies via the conductors 68 and 70 to a transformer 278 a pulse train related to the revolutions per unit time of the shaft 46 which is driven by the motor 42 under control of the motor controller 44. The outputs from the transformers 276 and 278 are compared and a signal is produced upon the conductors 72 and 74 to the motor controller 44 so as to maintain the predetermined ratio of input to output r.p.m.s.

Pulses are supplied by the reference tachometer 50 of the FIGURE 2 which includes the generating means 52, which for example, may be a ferrous gear with projecting teeth. The passage of the teeth past the pick-up head 54 generates a series of pulses which are applied to the transformer 276 of the FIGURE 5. One end of both the primary and secondary of the transformer 276 is at ground while the opposite end of the transformer 276 is coupled to the base of a transistor T8. A capacitor 280 and a diode 282 are connected in parallel between ground and the base of T8 and the diode 282 is poled in such a manner that the capacitor 280 is charged by positive pulses only. A resistor 284 is connected between ground and the emitter of T8 while a resistor 286 is connected between the collector of T8 and a source of positive voltage, such as +20 volts, as shown. The collector of T8 is coupled to the base of T9 through a capacitor 288. The emitter of T9 is coupled directly to ground while its collector is connected through a resistor 290 to the source of positive potential. The collector of T9 is coupled to the base of T10 through a series capacitor 292and diode 294 and a resistor 296 is connected between the common point of the capacitor 292 and the diode 294 and the source of positive potential.

With continued reference to the FIGURE 5, the emitter of T10 is connected directly to ground while its collector is connected to the source of positive potential through a resistor 298. A resistor 300 is connected between the collector of T10 and the base of T9 and is utilized to turn T9 oif after each pulse. The output of T10 on its collector is coupled through a series connected diode 302 and potentiometer 304 to a capacitor 306. A Zener diode ZDl is connected between ground and the collector of T10 and serves to limit the amplitude of the positive pulses from the collector of T10 which charge the capacitor 306 in a positive direction through the movable arm of the potentiometer 304 and a resistor 308 which is connected to the non-ground side of the capacitor 306. Thus, the reference tachometer 50 which is producing a signal indicative of the revolutions per unit time of the output shaft of the clutch 22 causes the capacitor 306 to be charged in a positive direction.

The circuitry associated with the feedback tachometer 62 in the upper portion of the FIGURE will be discussed and its purpose is to charge the capacitor 306 in a negative direction. After a minimum output adjustment has been set so as to provide the required ratio between the two shafts 46 and 48, then if the shafts are rotating at their prescribed revolutions per unit time, then the capacitor 306 will remain substantially uncharged. If one or the other shafts deviates from its prescribed revolutions per unit time (e.g., the output shaft speeds up) then the circuitry will function to compensate for the new revolutions per unit time and automatically adjust itself to maintain the prescribed ratio between the two shafts.

The circuitory in the upper portion of the FIGURE 5 and coupled to the transformer 278 is substantially identical to a portion of the lower circuitry except for the use of complementary transistors and oppositely poled diodes. For example, the input pulses from the feedback tachometer 62, which is substantially similar to the reference tachometer 50, are applied to the primary winding of the transformer 278 is coupled between ground and the base of the PNP transistor T11. The emitter of T11 is coupled to ground through a resistor 310. A parallel coupled capacitor 312 and diode 314 are connected between ground and the base of T11 and the diode 314 is poled in such a manner that the capacitor 312 is charged by negative pulses applied thereto. The collector of T11 is connected to a source of negative potential, such as -20 volts, through a resistor 316 and is coupled to the transistor T12 at its base by a capacitor 318. The emitter T12 is coupled directly to ground while its collector is connected to the source of negative potential through a resistor 320. The output developed across the resistor 320 is connected to the base of T13 through the series coupled capacitor 322 and diode 324. A resistor 326 is connected between the source of negative potential and the common point of the diode 324 and the capacitor 322.

The emitter of T13 is connected directly to ground while its collector is coupled to the source of negative potential by a resistor 328. A resistor 330 is connected between the collector of T13 and the base of T12 so as to turn T12 olf after each pulse. The negative pulses developed across the resistor 328 are applied to the capacitor 306 by the series coupled diode 332, potentiometer 334, through its movable arm, and a resistor 336. A Zener diode ZD2 is connected between ground and the collector of T13 so as to limit the amplitude of the negative pulses being applied to the capacitor 306.

The voltage condition of the capacitor 306 is indicated on the base of a transistor T14 whose collector is coupled to the source of positive potential. The emitter of T14 is coupled directly to the base of a transistor T15 whose emitter is connected to the movable contact of a minimum adjust potentiometer 338. The position of the movable arm of the potentiometer 338 will determine the minimum output speed of the motor 42 when the rewind is in a stalled condition, i.e., the reel is not turning but web tension is required. The speed ratio of the shaft 46 to the shaft 48 is set by adjusting the calibrate potentiometers 304 and 334. Experimentation will show the desired setting of the potentiometer 338 so that suflicient revolutions in excess of the shaft 48 are supplied by the shaft 46 but not such an excess as to provide heating, excessive wear, etc., of the clutch 22. The emitter of T15 is connected to a source of positive potential such as 37 volts, by a resistor 340. The potential developed across the resistor 340 is coupled to the base of a transistor T16 whose collector is also coupled to the source of positive potential. The emitter of T16 is coupled directly to the base of a transistor T17 whose collector likewise is connected to the source of positive potential. The emitter of T17 is coupled to ground through a resistor 342 which is by-passed by a diode 344 which absorbs the inductive effect of any inductive reactance developed across the resistor 342. The output to the motor controller 44 is provided on the conductors 72 and 74 which are coupled across the resistor 342. The motor controller 44 through the signals developed upon the conductors 72 and 74 control the electrical energy applied to the motor 42 which is transformed into rotational energy and applied to the clutch 22 by the shaft 46.

OPERATION In the embodiment which was constructed and operated in accordance with the teaching of the present invention, the rewind system maintained better tension control and produced a better roll of material whether the material be a heavy or a light web than any known previously available equipment. Previously known slow responding systems tend to produce eratic tension changes which leads to rolls with varying edges and tends to break webs of light material. Systems of this type do not permit a very great range in tension before instability problems of various types develop.

In the present invention, attention has been directed to all components of the loop so as to increase their response time to the maximum. The one area that cannot .be changed to any great extent is the inertia of the rewind shaft, the rewind roll and the coupling device. If

. of motor and generator fields is undesirable in that this type of control is extremely slow in response rate. By

employing a clutch of the type set forth in the invention it was found possible to increase the response rate of this part of the loop due to the relative small current required to energize the clutch. A filtered DC power supply along with transistorized circuitry aided in increasing the response rate even more. The result is an extremely fast responding, automatic tension control system that produces a reel of wound material, the bands of the material being sufliciently tight but not so tight ,as to cause telescoping of the reel.

During initial setting-up procedures for the system,

experience will dictate the optimum setting for the many controls in order to obtain etlicient operation of the system; however, the following is intended to be a general outline. With reference to the FIGURE 3, the switch is positioned upon its 01f contacts by placing the movable arms 144 and 148 upon those contacts. It will be noted that the movable arms 144 and 148 rotate together so that they will be at all times, upon similar contacts of their respective wafers 142 and 146. The operate switch 94 would be opened so that the resistance 136 would be in series with the output so as to minimize any possible damage to the meter '32 during calibration procedures. In addition, with the operate switch 94 open, ,the sensitivity of the meter 32 would be decreased so that ,during setting-up procedures one would not unintentionally go past a null or zero point of the meter.

Next, the arms 144 and 148 of the switch 140' would be placed at their A contacts. This removes the output from the load ring A by applying ground to the conductor 96 through the conductor '82 and movable arm ,144. In this manner, the load ring B can now be adjusted. Any rough adjustment may be formed by moving the iron core of the differential transformer of the load ring "and after adjusting for a null at zero volts, the movable arm of the potentiometer 122 would be adjusted so that the member 22 reads zero.

Next, the movable arms 144 and 148 would be advanced to their '3 contacts so-that the output from the load ring B is now out of the circuit (output to ground) and the output from the load ring A is now in the circuit. After a similar mechanical adjustment (not shown) is performed uponthe load ring A as was suggested and described for the load ring B, the movable arm of the potentiometerg98 would be adjusted until the meter 32 reads zero. In the next step of the procedure, the movable arms 144 and 148 would be advanced to their A+B contacts so that the output from both load rings A and B are not grounded. The operate switch 94 is now closed so that the high resistance 136 is removed from the circuit. The meter 32 should still read almost zero.

Initially, it will be understood that the oscillator 134 would be operating and inductiviely coupled from the primary winding 129 to the secondary winding 127. The frequency of the oscillator 134 may be that found most expedient; however, in the preferred embodiment, the frequency of the oscillator 134 was 5,000 cycles per second. Thus, output from the load rings A and B would modulate the signals from the oscillator 134. The movable arms 144 and 148 of the switch 140 are now positioned upon their operate contacts as shown in the FIGURE 3. In the operate position, currents are fed through the capacitor 158 and the potentiometer 160. These currents are phase-shifted 90 from each other and each can be changed in amplitude and shifted 180 by adjusting the potentiometers 130 and 132. This permits obtaining a final precise zero on the meter 32 with no load or web in the machine. It will be noted that the circuit is now complete from one end of the primary winding of the transformer 112, through the conductor 114 to the secondary winding of the load ring B and from the opposite end of the primary winding of the transformer 112 to the conductor 138, switch 94, conductor 96 and to the secondary windings of the load ring A. The input balance circuit and both of the differential transformer (the load rings A and B primaries are fed from the secondary winding 127 of the transformer 128 which is applied to the conductor 96 by the conductor 152.

The movable arm 156 of the potentiometer 130 and the movable arm 160 of the potentiometer 132 may be adjusted so as to buck out any residual null voltage so as to obtain a zero reading on the meter 32 without a web being advanced. Subsequently, a spring scale (not shown) calibrated in pounds may be used to measure the tension of the web so that the movable arm 190 of the calibrate adjust potentiometer 184 may be positioned so as to read the pounds directly upon the meter 32. Of course, it will be understood that the meter 32 would have a face plate indicating pounds or a numbering system which can be related to pounds. The calibration in pounds is, of course, not necessary but acts only to serve as a convenience in the operation of the system.

Although the calibration and settling-up procedures are being described with reference to the figures in successive order, it will be understood that the. preferred order may vary from this or it may even be found convenient to simultaneously make adjustments to the controls anywhere in the system. Once the initial setting-up procedures have been established and the controls of the system so adjusted, little, if any, adjustment to the rewind system will be necessary.

Next, with reference to the FIGURE 4, the adjustments to the clutch control circuitry will be set forth.

Qil

Previously, the circuitry illustrated on FIGURE 4 has been identified as a salient feature of the invention and wherein a low gain amplifier, including the transistor T7 and its associated circuitry, will control the current through the clutch 22 with the input from the tension sensores of the FIGURE 3 on the conductors 24 and 26 and applied to the transistor stages T4, T5 and T6. The maximum gain of the circuitry is relatively low and therein in provides a system whereby partial correction of tension errors is effected and does not provide a constant tension or a constant torque procedure which has been described as undesirable. The apparatus of 1 the present invention provides a system somewhere between a constant torque and a constant tension system, the closeness of the present invention to a constant torque or a constant tension system being determined by the adjustment of the taper adjust control 226.

If a reel of relatively light material is to be wound, then the tension range transformer 246 of the FIGURE 4 would be set at the 20 volt or 40 volt position by contact with the movable arm 252. If relatively heavier webs are to be wound and reeled, then the movable contact 252 would be moved to either the 60 volt or volt contact. The taper adjust potentiometer 226, which determines the gain of the amplifier, would have its movable arm 228 set some place at about its mid-point and if it is later discovered that the tension of the material on the outside of a full roll is too great, then the amount of resistance in the circuit could be increased by moving the movable arm 228 upwardly and thus adding additional resistance from the potentiometer 226. Similarly, if the material upon the reel was found to be too loose, on the outside of a full roll, then the resistance in the circuit could be re duced by the potentiometer 226.

.The initial tension (meaning the tension at start of a new roll) adjusment is provided by the potentiometer 212 and similar to the adjustment of the taper adjust potentiometer 226, would be set somewhere near its midpoint for initial operations and altered accordingly if found desirable.

The function of the rectifier 260 is to rectify the alternating current supplied to the transformer 254 and to deliver a direct current through the clutch winding 22 to provide for minimum clutch tension. The potentiometer 266 through its movable arm 274 will determine the amplitude of the current through the clutch 22 and is used to balance out residual friction that could cause the reel 20 to stall. The minimum tension adjustment potentiometer 266 is adjusted until the point is reached where the reel 20 will just maintain its speed with no web or control signal.

As the tension sensors of the FIGURE 3 generate an analog signal on the conductors 24 and 26 (the added output voltages from the load' rings A and B) the signal will be applied to the base of the transistor T4 and through the three emitter-follower stages comprising the transistors T4, T5 and T6 to the base of the transistor T7. As the signal applied to the conductors 24 and 26 varies, so will the current through the clutch 22, The minimum tension adjust potentiometer 266 will supply current through the clutch winding 22 until the potential drop of the controlling circuit exceeds the potential drop of the minimum tension circuit. Thereafter, the current is maintained through the clutch 22 in such a manner that a web of material is wound upon the reel 20 hav ng the desired characteristics of web tension. In general, the web tension will decrease as the diameter of the reel increases so that a condition of telescoping will not manifest itself.

The circuit of the FIGURE 5 is utilized to operate the motor 42 and the motor controller 44 in such a manner that the motor 42 delivers sufficient rotation per unit time upon its shaft 46 to the clutch 22 that will meet the requirements of the rotational energy to be supplied to the clutch output shaft 48. In other words, the shaft .46 is malntained at revolutions per unit time exceeding the revolutions of the shaft 48 but to not such a degree as to waste power and cause heating, excessive wear, etc. to the clutch 22. By experimentation, it has been found that if the input shaft 46 is maintained at approximately 110% of the output shaft 48, then sufficient torque is always available without the presence of the deleterious effects set forth. The minimum output adjust potentiometer 338 of the FIGURE is positioned to give minimum output on the conductors 72 and 74 with zero input across the capacitor 306. A pulse train is delivered by the tachometers 50 and 62 to the circuitry of the FIGURE 5 wherein the spacing between the pulses is indicative Of the revolutions per unit time. The closer the spacing between the pulses, the faster the shaft is operating.

The pulse train from the reference tachometer 50 is applied to'the transformer 276 and noting the polarity of the diode 282, only positive pulses are applied to the base of the transistor T8. The transistors T9 and T10 act as a one-shot multivibrator and the resistor 300 coupled from the collector of T10 back to the base of T9 assists in turning T9 off after each pulse. ZD1 limits the amplitude of the positive pulses from T10 and the positive pulses are used to charge the capacitor 306 in a positive direction. In a similar manner, signals from the feedback tachometer 62 are applied to the base of the transistor T11 and, noting the polarity of the diode 314, only negative pulses will be amplified and applied to trigger the one-shot multivi-brator formed by the transistorsTlZ and T13. Likewise, ZD2 limits the amplitude of the negative pulses so that the negative pulses are used to charge the capacitor 306 in the opposite or negative direction. Adjustment of the calibrate otentiometers 304 and 334 will provide at the output conductors 72 and 74, sufiicient voltage to maintain the proper control of the motor 42 without the creation of excessive heat due to excessive slip of the clutch 22.

Again, it is stated that various operating parameters may be adjusted or changed as are found expedient and as experienced in the winding of the reels of various weights, grades and thicknesses is achieved. However, it is to be emphasized that the system demonstrates extremely stable operation along with a fast responding automatic tension control system capable of proudcing rolls of a superior nature.

Thus, the present invention may be embodied in other specific forms without departing from the spirit and the essential characteristics of the invention. It will be understood that other types of clutches, amplifiers and control circuits may be employed. For example, vacuum tubes could be substituted for the transistor circuitry. The present embodiment is, therefore, to be considered in all respects as illustrative and the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of the equivalency of the claims are, therefore, intended to "be embraced therein.

What is claimed is:

1. Apparatus for controlling the winding and unwinding of a continuous length of material upon a rotary reel with a varying tension comprising means for applying tension to the length of material, means for directly sensing the tension of the material adjacent the reel for generating a signal related to the tension and tension correction means responsive to the generated signal for controlling said means for applying tension in response to the generated signal from said means for sensing, said correction means including means connected with said means for applying tension for effecting compensation for changes in tension less than required to provide application of a constant tension by said means for applying tension.

2. Apparatus according to claim 1 wherein saidmeans connected with said means for applying tension comprises low-grain feed-back control means for providing feed-back control insufiicient to elfect complete compensation for tension variations, said feed-back control means including a low-gain amplifier for controlling the tension of the material being wound upon the reel, and means coupled to said amplifier and responsive to the generated signal from said means for directly sensing and controlling the amplifier current to thereby control the tension of the material.

3. Apparatus for controlling the tension of a continuous length of material extending from a rotary reel with a varying tension comprising means for directly sensing the tension of the material adjacent the reel for generating a signal related to the tension, feedback control means responsive to said means for sensing for elfecting only partial compensation for tension variations and including a low gain transistor amplifier for controlling the tension of the material extending from the reel, and means in circuit with said amplifier and responsive to the generated signal from said means for sensing for providing an input to said amplifier to thereby control the tension in said material and provide gradual tension alteration therein.

4. The combination as defined in claim 3 including means in circuit with said amplifier for varying the degree of gradual tension change in siad material by manually controlling the gain of the amplifier.

5. Tension control apparatus for use with a continuous length of material and a rotary material accommodating reel for applying a varying tension to the material and comprising a clutch engageable to apply rotary motion to said reel, means for directly sensing the tension of the material, feed-back circuit means responsive to said means for sensing for varying the coupling of said clutch upon alteration of said tension, said feed-back circuit means including means for providing low-gain therein to effect less than full compensatory alteration in the coupling of said clutch and providing gradual alteration in the torque applied to said reel.

'6. The combination as defined in claim 2 wherein said clutch is a current responsive electromagnetic clutch electrically connected with said feed-back circuit means.

7. A clutch control system for an electrically controllable clutch comprising a low gain amplifier in circuit with said clutch, a source of potential coupled to said clutch and said amplifier, means controlled by the degree of coupling of said clutch for generating an output signal,

and means coupled to said amplifier for receiving said signal and for controlling the current of said amplifier according to the magnitude of said signal, said source of potential, amplifier, means controlled by said clutch, and means coupled to said amplifier defining a low-gain feed-back control system for providing clutch coupling control less than indicated by said output signal.

8. A clutch control system according to claim 11 wherein said amplifier comprises a low-gain transistor amplifier coupled in a common emitter configuration, said clutch being connected to the transistor emitter, said source of potential being coupled between said clutch and the collector of said transistor, and signal means for receiving said output signal comprising means coupled to the base of said transistor and adapted to receive said signal for controlling the current of said transistor amplifier in dependance upon the signal received.

9. A clutch control system including an electromag netic clutch having a coil for controlling the coupling between the input and output thereof and comprising a transistor amplifier including a transistor coupled in a common emitter configuration wherein said clutch is connected in series to the transistor emitter, a source of potential coupled between said clutch and the collector of said transistor means under control of said clutch for generating an output signal, means coupled to the base of said transistor and adapted to receive said signal for controlling the current of said transistor amplifier according to the magnitude of said signal and manual gain varying means coupled in series between said clutch and said emitter for controlling the degree of wariations in clutch coupling in response to the magnitude of said signal; said transistor amplifier, said source of potential, said means under the control of said clutch and said means coupled to the base of the transistor defining a low-gain feed-back control system for providing clutch coupling control less than indicated by said output signal.

10. A clutch control means for controlling the coumeans for electrically varying the coupling between the input and output of said clutch; said control means comprising a transistor amplifier including a transistor, said electrical coupling control: means of said clutch being connected to the emitter-collector circuit of said transistor, a source of potential coupled between said electrical coupling control means and the emitter-collector circuit of said transistor, means under control of said clutch for generating an output signal, means coupled to the base of said transistor and adapted to receive said signal for controlling the current of said transistor amplifier according to the magnitude of said signal to control the coupling of said clutch and means for supplying a predetermined fixed minimum current to said electrical coupling control means in the absence of an output signal from said means under control of said clutch to provide a minimum coupling between the input and output of said clutch; said control means defining a low-gain feed-back control system for providing clutch coupling control less than indicated by said output signal.

11. The combination as defined in claim 10 wherein said means for supplying a minimum current is a power supply whose output to said clutch is controlled by a potentiometer, said power supply being connected in parallel across said electrical coupling control means of said clutch, and said transistor having its emitter-collector circuit connected in series with said coupling control means.

12. Apparatus for controlling the tension of a continuous length of material extending from a rotary reel with a varying tension comprising means for producing rotary motion, electrically controllable means for cou pling said means for producing rotary motion to rotate said reel, means for sensing the material tension in the material extending from said reel, and means connected with and responsive to said means for sensing for controlling the degree of coupling of said means for coupling said means for producing rotary motion of said reel, said means for controlling the degree of coupling comprising means for varying the energization of said means for coupling, means connected with said means for varying the energization for determining the range of energization provided by said means for varying the energization to determine the range of tension applied to said material, and means seperate from said means for varying the range for applying an input signal to said means for varying the energization and including tension adjusting means for varying the magnitude of the input signal derived from said means for sensing,

13. Apparatus according to claim 12 wherein said means for varying the energization comprises a low gain;

amplifier having an output controlled by said means for applying an input signal, said tension adjusting means comprising means for comparing a reference signal With a signal derived from said means for sensing.

14. The combination as defined in claim 13 wherein the maximum gain of said amplifier is greater than unity and including means for adjusting the gain of said amplifier.

15. Web tension control apparatus for controlling the tension applied to a continuous web of material during the winding thereof upon a rotary reel comprising means for producing rotary motion, an electromagnetic clutch for coupling said means for producing rotary motion to said reel, means for directly sensing the material tension adjacent said reel, and feed-back means coupled to and controlled by said means for directly sensing the material tension, said clutch being electrically connected with said feed-back means and said feed-back means comprising means to control clutch energization from said means to produce rotary motion for providing a gradually decreasing tension in said web.

16. Apparatus according to claim 15 wherein said feedback means includes a transistor amplifier arranged in a common emitter configuration, said clutch being included in the emitter-collector circuit of said amplifier, and said means for sensing the material tension adjacent said reel being coupled to said amplifier for providing an input thereto controlling the energization of said clutch.

17. The combination as defined in claim 16 including means to supply sutficient current to said clutch for providing a minimum degree of coupling in said clutch upon a predetermined reduction in the energization provided to said clutch by said amplifier.

18. The combination as defined in claim 17 wherein said means to supply sufiicient current to said clutch is a power supply controlled by a potentiometer and connected in parallel with the electrical input to said clutch, said emitter-collector circuit of said amplifier being connected in series with the electrical input to said clucth.

19. The combination as defined in claim 16 including means for varying the potential coupled between said clutch and said collector to thereby control the range of the magnitude of energization of said clutch for determining the range of tension applied to said material.

20. Apparatus for controlling the winding and unwinding of a continuous length of material upon a rotary reel comprising means for producing rotary motion, means forcoupling said means for producing rotary motion to rotate said reel, means for directly sensing the material tension adjacent said reel, means under control of said means for directly sensing tension for determining the degree of coupling of said means for coupling, circuit means including a low gain amplifier whose current is controlled by said means for directly sensing tension for energizing said means for coupling in accordance with the current of said amplifier to effect less than full compensatory alteration in coupling, means for sensing the revolutions per unit time of said reel, and means coupled to said means for sensing the revolutions controlling said means for producing rotary motion for causing the revolutions per unit time to exceed the revolutions of said reel.

21. The combination as defined in claim 20 wherein the ratio of the revolutions of said means for producing rotary motion to said reel revolutions is approximately 11 to 10.

22. Apparatus for controlling the winding and unwinding of a continuous length of material upon a rotary reel comprising means for producing rotary motion, means for coupling said means for producing rotary motion to rotate said reel, circuit means including a transistor amplifier arranged in a common emitter configuration, said means for coupling being a clutch included in the emittercollector circuit of said amplifier, means for directly sensing the material tension adjacent said reel for controlling said amplifier to effect less than full compensatory alteration in coupling and thereby control the energization of said clutch, a first tachometer coupled to indicate the revolutions per unit time of said reel, a second tachometer coupled to indicate the revolutations per unit time of said means for producing rotary motion, and means for maintaining a predetermined ratio between the revolutions of said reel and said means for producing rotary motion.

23. The combination as defined in claim 22 wherein said means for maintaining the predetermined ratio comprises means for comparing the outputs of said tachometers coupled to means for controlling said means for producing rotary motion.

24. Apparatus for controlling the winding and unwinding of a continuous length of material upon a rotary reel with a gradually varying tension comprising means for directly sensing the tension of the material adjacent the reel, means for generating a signal related to the tension so sensed, and means for applying rotary motion to the reel in accordance with the magnitude of the generated signal and at a level insufiicient to compensate fully for tension variations in the material.

25. Web tension control apparatus for use with a continuous web of material and a web accommodating reel, the apparatus comprising reel drive means, variable coupling means for couplingsaid drive means to said reel, web tension sensing means for directly sensing and indicating variations in tension in said web, feed-back means connected between said tension sensing means and said coupling means for controlling the degree of coupling of said coupling means, said feed-back means comprising means responsive to web tension variation indications from said tension sensing means for all partially compensating for such variations by altering the coupling of said coupling means less than required to maintain a constant tension on said web.

26. Web tension control means for use with a continuous web of material and a web accommodating reel; said apparatus comprising reel drive means, electrically controllable clutch means for coupling said reel to said drive means, web tension sensing means for directly sensing web tension, feed-back means controlled by said tension sensing means and connected with said clutch References Cited UNITED STATES PATENTS 2,990,484 6/1961 Jones 3l094 3,073,977 11/1963 Ames 31094 3,114,850 12/1963 Hansen 310-94 3,157,807 11/1964 Kimberly 3l095 3,160,802 12/1964 Abell 318-6 3,223,906 12/1965 Dinger 3187 3,241,785 3/ 1966 Barrett 24275.51 3,348,107 10/1967 Hamby 3186 3,207,950 9/1965 Smith 31095 X B. DOBECK, Primary Examiner A. G. COLLINS, Assistant Examiner US. Cl. X.R. 318-6 

